Selective Pharmacogenetic Activation of Catecholamine Subgroups in the Ventrolateral Medulla Elicits Key Glucoregulatory Responses

Abstract

Catecholamine (CA) neurons in the ventrolateral medulla (VLM) contribute importantly to glucoregulation during glucose deficit. However, it is not known which CA neurons elicit different glucoregulatory responses or whether selective activation of CA neurons is sufficient to elicit these responses. Therefore, to selectively activate CA subpopulations, we injected male or female Th-Cre+ transgenic rats with the Cre-dependent DREADD construct, AAV2-DIO-hSyn-hM3D(Gq)-mCherry, at one of four rostrocaudal levels of the VLM: rostral C1 (C1r), middle C1 (C1m), the area of A1 and C1 overlap (A1/C1), and A1. Transfection was highly selective for CA neurons at each site. Systemic injection of the Designer Receptor Exclusively Activated by Designer Drugs (DREADD) receptor agonist, clozapine-N-oxide (CNO), stimulated feeding in rats transfected at C1r, C1m, or A1/C1 but not A1. CNO increased corticosterone secretion in rats transfected at C1m or A1/C1 but not A1. In contrast, CNO did not increase blood glucose or induce c-Fos expression in the spinal cord or adrenal medulla after transfection of any single VLM site but required dual transfection of both C1m and C1r, possibly indicating that CA neurons mediating blood glucose responses are more sparsely distributed in C1r and C1m than those mediating feeding and corticosterone secretion. These results show that selective activation of C1 CA neurons is sufficient to increase feeding, blood glucose levels, and corticosterone secretion and suggest that each of these responses is mediated by CA neurons concentrated at different levels of the C1 cell group.

Arginine-vasopressin mediates counter-regulatory glucagon release and is diminished in type 1 diabetes

“…Catecholaminergic neurons in the VLM are a key component of the central counterregulatory circuit and the ability of these neurons to evoke hyperglycaemia (Ritter et al, 2000;Zhao et al, 2017;Li et al, 2018) and hyperglucagonaemia (Andrew et al, 2007) is well-established. Recent studies have clearly demonstrated that spinally-projecting C1 neurons evoke hyperglycaemia by stimulating the adrenal medulla (Zhao et al, 2017;Li et al, 2018), suggesting that the response is likely to be mediated by corticosterone and/or adrenaline. We also show that activation of A1/C1 neurons evokes hyperglycaemia, but by promoting glucagon release.…”

“…Many physiological stressors activate hindbrain catecholamine neurons, which release noradrenaline (A1) or adrenaline (C1) and reside in the ventrolateral portion of the medulla oblongata (VLM). Activation of C1 neurons (by targeted glucoprivation or chemogenetic manipulation) is known to elevate blood glucose (Ritter et al, 2000;Zhao et al, 2017;Li et al, 2018) and plasma glucagon (Andrew et al, 2007). Furthermore, C1 cell lesions severely attenuate the release of AVP in response to hydralazine-evoked hypotension (Madden et al, 2006), indicating that this hindbrain site may be a key regulator of AVP neuron activity during physiological stress.…”

Regulation of perceptual learning by chronic chemogenetic manipulation of parvalbumin-positive interneurons

“…Future studies could also help determine whether these measures are correlated with PV expression. Although this matter was beyond the scope of this study, based on previous studies (Wirtshafter and Stratford, 2016;Li et al, 2018;Cisneros-Franco and de Villers-Sidani, 2019), a correspondence between the specific chemogenetic manipulation and PV staining intensity is to be expected. In addition, future studies are needed to determine whether the role of PV-related inhibition on auditory discrimination abilities is lateralized.…”

“…Following dura removal with a 27-G needle, 1 μL virus (pAAV-hSYN-DIO-hM4D(Gi)-mCherry or pAAV-hSYN-DIO-hM3D(Gq)-mCherry was injected using a precision syringe pump (PHD Ultra 4400, Harvard Apparatus, Holliston, MA) at a rate of 0.05 μL/min. The surgical wound was sutured and cleaned, the rat was monitored until full recovery and medicated with antibiotic (enrofloxacin, 10 mg/kg, s.c.) and analgesic (carprofen, 5 mg/kg, s.c.) for at least 3 days (Wirtshafter and Stratford, 2016;Li et al, 2018).…”

Hypoglycemia: Role of Hypothalamic Glucose-Inhibited (GI) Neurons in Detection and Correction

“…Glucose sensors in the hindbrain and PMV are critical for the CRR as detailed in several comprehensive review articles (Ritter et al, 2011 ; Routh et al, 2012 ; Donovan and Watts, 2014 ). Ritter and colleagues show that specific clusters of catecholamine neurons within the C1 cell groups (C1r, C1m, A1/C1) of the rostral ventral lateral medulla (RVLM) in rodents are essential for individual components of hypoglycemia correction including epinephrine and corticosterone secretion as well as glucoprivic feeding (Ritter et al, 1981 , 1998 , 2001 , 2006 ; Li et al, 2017 ). The feeding and corticosterone response is mediated by forebrain projections to hypothalamus (i.e.…”